This invention relates to the processing of semiconductor devices, and more specifically, to a low temperature formation of palladium silicided shallow junctions using implant through metal/silicide technology.
The short channel effect has become a dominant constraint in the development of high density semiconductor integrated circuits (ICs). In order to suppress the short channel effect, a shallow junction structure is utilized in place of conventional junction structures in semiconductor devices of high density ICs. A semiconductor device with the shallow junction structure can operate normally as its channel length decreases to a critical dimension, thus improving the performance of high density ICs.
However, since P-type impurities, such as boron ions, have a higher diffusion coefficient, heavily doped P-type diffusion regions in a N-type silicon substrate are not easily controlled. That is, it is difficult to keep the P.sup.+ -N junction depth in a small range. Moreover, a conventional method for forming a junction is carried out by implanting ions directly into the silicon substrate. The requisite high-temperature annealing process for this enhances the diffusion of the impurities in the substrate, thus failing to form the shallow junction.
One solution to the above mentioned problems is to implant boron ions into the silicon substrate using a low energy ion implanter. The low energy ion implanter implants ions at a low implanting energy of 1-2 KeV, or even as low as 200-500 eV. However, though shallow junctions can be formed through the low implanting energy, the manufacturing costs are increased due to the introduction of the special implanter. Furthermore, because the diffusion regions formed by the low-energy ion implantation has a high sheet resistance, this method can not be applied in the fabrication of high density ICs.
Another solution is to implant silicon or germanium ions into the silicon substrate, thus forming an amorphous surface thereon. The amorphous surface can prevent the diffusion of boron ions due to the elimination of the channel effect. However, a very high temperature annealing process is necessary for the recrystallization of the damaged substrate surface. The high temperature process does not conform to the requirements for fabricating the high density ICs. Furthermore, in order to have an acceptable surface properties, the process conditions must be strictly controlled. Therefore, this method is not suitable for the semiconductor industry.